The present invention relates to image generation, and more particularly, to apparatus that provides for multiple level occulting using a mask buffer that may be employed in an image generator.
One problem relating to image generation is that conventional visual systems suffer image or frame rate degradation as a function of the height of a vantage point above a terrain surface or the number of moving models present in an image scene. In addition, conventional visual systems suffer frame rate degradation as a function of environment complexity such as viewing within a complex urban setting. In regions of an image containing rugged terrain or many cultural features, depth complexity increases significantly as the height of the eye (or viewing) point approaches the terrain surface. This is a fundamental reason that image generators designed for use as flight simulators suffer pixel overload in ground applications.
Visual systems that are optimized for use as air vehicle simulators solve polygon occulting problems off-line for fixed objects such as land, natural features, and cultural features. One frequently used polygon sorting technique is generally known as a binary separation plane method. If all objects are fixed, this technique is excellent for complex, ground based scenes. However, when faced with moving models, such approaches must then augment the off-line occulting process with a pixel-level occulting process such as Z- or R- buffering. Because such an architecture is not optimized for extensive real-time occulting, frame rate reduction may be used to resolve depth complexity when faced with many moving models. A slower and irregular frame rate has potential for a negative training impact, especially for gunnery tasks, since gunnery is a task during which a large number of moving targets can be expected to predominate in the scene.
The frame rate of an image generator using mixed occulting including off-line binary separation plane and real-time R-buffer techniques degrades as the number of dynamic objects in the scene increases. There is a relatively rapid fall-off in frame rate as the dynamic object content increases beyond its design point, typically about 30%. If the image generator is to be modified to handle a much larger percentage of moving models, the pixel processor and bus structure must be dramatically upgraded. As such, the image generator may as well be designed for 100% real-time occulting from the start.
Therefore, it is an objective of the present invention to provide for apparatus for use with an image generator that performs real-time occulting of all objects, whether fixed or moving.